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Japan gets on top of the paper work

THE JAPAN Pavilion at Expo 2000 in Hanover, Germany could be described as unique, both in its construction and in the way this reflects the theme of the exhibition; minimising the use of resources and carbon dioxide. Commissioned by Japan External Trade Organisation and designed by Japanese architect Shiguru Ban who has an international reputation for using these materials - the 35m clear span structure is constructed from a core of paper tubes clad with lightweight paper and polymer coated polyester membranes.

The Pavilion embraces three elements: an approach zone, the exhibition space and ancillary office accommodation. The temporary nature of the structure led to the use of paper tubes, allowing minimal waste of materials. At the end of Expo the site will return to its original use as a car park.

The approach is constructed from conventional steel, easily recycled. The office spaces are housed in re-usable containers. However, for most visitors to the Pavilion, the main experience of the structure comes when entering the 2,000m 2exhibition hall.

The enclosed space is 72m long and varies in width and height. The interior is enclosed by the highly articulated gridshell structure. At its widest point, the structure spans 35m, and is 15.5m high. Visitors enter the hall at first floor level, moving down a ramp that runs along almost the full length of the building.

The initial idea was to push up a double curved gridshell from a grid of paper tubes to form the armature. Consultant to the project, Professor Frei Otto, brought in Buro Happold as structural engineer.

Happold commissioned a series of tests, and buckling analysis identified a requirement for increased out-of-plane stiffness. A simple calculation backed by further tests showed that the required stiffness would have needed tubes of such a size that the bending process would have been almost impossible, with a very high risk of damage.

The solution was a structure placed on top of the gridshell armature to support the cladding system on a 3m grid.

Timber ladders were introduced at 3m centres across the width of the hall, with single timber purlins running longitudinally along the building, also at 3m centres. Undertying these cladding support ladders by a chorded array of small diameter tie cables gave the additional bending stiffness.

The 120mm diameter paper tubes on a 1m diagonal grid are connected to each other and to the timber above with simple tied fabric bands. Over this network are the cladding ladder arches, stiffened with underslung 8mm cables.

Four 125mm by 60mm laminated timber sections are used in each ladder.

These are connected together with shear blocks to generate a single bending stiff element. Longitudinally 60mm by 95mm purlins pass through the ladders making the total depth of the timber structure 180mm. These longitudinal members work compositely with an additional timber packer required to bring the top of the purlin level with the ladders.

The cladding alternates between a double membrane of paper with a protective cover of polymer coated polyester between ladders and single clear polymer coated polyester membrane in the gutters.

At the foundation the timber ladders and paper tubes are connected to steel frames which sit directly on the ground and are weighted with sand, thus avoiding the use of concrete.

The ends of the hall are closed and stiffened with vertical cable nets arranged on the diagonal. Each net is tensioned between a laminated timber end arch and the foundation.

The laminated timber sandwiches the paper tubes and provides stiffness to the lip of the structure, allowing attachment of the cable system. 12mm diameter cables are arranged to form a series of equilateral triangles into which timber and paper honeycomb board composite panels wereare fixed. These are then covered with paper or PTFE glass membranes.

Construction began in January of this year, with the paper tubes laid out flat on a temporary scaffold. This was then used to push the paper grid into the final shape, over a period of three weeks. Once in its final form, the pre-curved timber structure was lifted into position and connected to the paper tubes with fabric bands. Work started in the centre of the building and proceeded towards both ends simultaneously.

When the timber over the central hump was complete, lacing of the lightly prestressed cables began, with attachment of the membrane following closely behind. Once six timber lines had the cables installed they were de-propped and the structure stood by itself for the first time. Work then proceeded in waves working towards the ends of the building.

Client: Japan External Trade Organisation

Architect: Shigeru Ban Architect

Architectural consultant: Professor Frei Otto

Structural engineer: Happold Ingenieurburo + Buro Happold

Constructor: Takenaka Europe

Paper tubes: Sonoco

Timber: Merz + Kaufmann

Cladding membranes: TSP Taiyo

Cables: Pfeifer Seil-und Technik

Materials testing: Institut fur Bauforschung, University of Dortmund

Erection scaffolding: Peri

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